1. Field of the Invention
The present invention relates to a light emitting diode (LED) drive apparatus, and particularly to an LED illumination apparatus.
2. Description of the Related Art
Recently, a light emitting diode drive apparatus for driving a light emitting diode has developed and put to practical use. A conventional light emitting diode drive circuit disclosed in Japanese Patent Laid-Open No. 2001-8443 will be described below with reference to FIG. 13. The conventional light emitting diode drive circuit includes a light emitting diode 102, a coil 103 connected to the light emitting diode 102 in series, and a diode 104 connected to the light emitting diode 102 and the coil 103 in parallel. The diode 104 supplies a back electromotive force generated in the coil 103 to the light emitting diode 102.
A direct-current power supply 101 is further provided to apply a pulse voltage to the light emitting diode 102, the coil 103, and the diode 104. A switching element 105 which switches between application and non-application of an output voltage of the direct-current power supply 101 is connected between the light emitting diode 102 and the direct-current power supply 101. For example, the switching element 105 includes a switching transistor and an oscillator. A cathode of the diode 104 is connected to a positive electrode of the direct-current power supply 101 such that a reverse bias is applied to the diode 104.
In the conventional light emitting diode drive circuit, when the switching element 105 is turned on, the direct-current power supply 101 applies the output voltage to the light emitting diode 102 to cause the light emitting diode 102 to emit light. When the switching element 105 is turned off, the light emitting diode 102 emits light by using the back electromotive force of the coil 103.
The conventional light emitting diode drive apparatus has the following problems. The light emitting diode 102 is a capacitive load. In the commercial light emitting diode, a capacitor or a zener diode as an electrostatic protective element is generally connected to the light emitting element in parallel in order to prevent electrostatic discharge damage. Therefore, when the switching element 105 is turned on to transfer a period from a current cutoff period to a current passage period, a fluctuation in potential at a low-potential-side terminal P2 of the coil 103 is increased. At this point, large current flows instantaneously into a parasitic capacitance of the light emitting diode 102 or parasitic capacitances of the capacitor or the zener diode which are connected in parallel to the light emitting diode 102 as the electrostatic protective element. As a result, a forward voltage is instantaneously decreased in the light emitting diode 102. The light emitting diode 102 becomes a noise generating source because the voltage fluctuates between both terminals of the light emitting diode 102. Because this phenomenon is generated in each time when the switching element 105 is turned on, the conducted emission transmitted to the direct-current power supply 101 is increased. Furthermore, when the forward voltage is decreased in the light emitting diode 102, the current flows into the parasitic capacitance to decrease the current flowing into the light emitting diode 102. As a result, sufficient luminance is not obtained.
In view of the foregoing, an object of the invention is to provide a light emitting diode drive apparatus which can decrease the conducted emission with a simple configuration.